The invention relates to a camshaft adjuster for an internal combustion engine having hydraulic medium guides.
To reduce fuel consumption and the emission of untreated gases, as well as to increase power and torque, diesel engines are generally fitted with camshaft adjusters. These adjusters change the phase position of the camshaft relative to the crankshaft. Currently, hydraulic vane cell adjusters having working chambers are used, in most instances. The adjustment is made via the controlled entry of oil into the chambers of the vane cells, from the engine circuit, via a control valve. The control valve is moved by means of an electromagnetic device.
A camshaft adjuster of this type, for an internal combustion engine having hydraulic medium channels, is known from DE 40 19 766 C2 which relates to a corresponding U.S. Pat. No. 5,273,007 the disclosure of which is hereby incorporated herein by reference. The camshaft adjuster, which is fitted with an axial adjustment piston, can be controlled with hydraulic medium channels, to adjust the angle of a camshaft. This reference describes a connection of the hydraulic medium channels from the camshaft bearing to a related adjustment chamber, in each instance. However, with this disclosure, the control of the camshaft adjuster is not described. The channel design of the hydraulic medium channels includes at least two channels. This design includes coaxially arranged channels that make a transition into a ring gap, in each instance, and form a variant that causes restrictions via production technology. The ribbed insert shown has the disadvantage that the stream of oil must flow around many edges, which are disadvantageous in terms of flow technology, and this results in disadvantageous oil foaming, particularly due to the rotating camshaft. In addition, the proposed embodiment shown as a plastic part does not ensure any permanent, fixed seat in the camshaft, because of creep at the engine operating temperature. Furthermore, the ribs shown, in combination with the ring grooves, cause a complicated die embodiment in an injection-molding die.
A camshaft adjuster for an internal combustion engine having hydraulic medium guides is also known from DE 199 18 910 A1 with a corresponding U.S. Pat. No. 6,053,139 the disclosure of which is hereby incorporated herein by reference. Using the hydraulic medium guides, it is possible to control a setting unit by way of a control valve, to adjust the angle of a camshaft. In this case, the setting unit has an inner body connected with the camshaft so as to rotate with it, and an outer body mounted to rotate relative to the camshaft, by way of which a drive connection runs from the crankshaft to the camshaft. The hydraulic setting unit has hydraulic medium applied to it, in targeted manner, by way of the control valve that is fixed in place relative to the camshaft. The control valve has a control piston that is guided in a central straining screw, so as to be displaced in the axial direction relative to the central straining screw. The inner body is braced axially against the camshaft by way of the central straining screw. The hydraulic medium guides are formed in the camshaft, whereby a hydraulic medium guide is arranged around the central straining screw. Accordingly, there is a relatively high level of machining effort for channels in the camshaft that carry hydraulic medium, i.e. in components adjacent to the camshaft.
An improved embodiment of the design of the hydraulic medium channels is known from DE 363862 A1, in the form of a tube that is pushed into the camshaft. However, this has the disadvantage of a very limited channel design, which can only be used with certain restrictions for supplying hydraulic medium to a camshaft adjuster.
In reference WO 0149978 A1, there is disclosed a simplified configuration of hydraulic medium channels which is represented via an insert piece having grooves that run in an axial direction, in interaction with the inside wall of the camshaft. This design has the disadvantage that the insert part must have a high level of dimensional accuracy, if independent channels are formed in adjacent grooves, in order to provide a secure seal. This is particularly difficult to accomplish with the specific embodiment disclosed, which has a formed sheet-metal part. Furthermore, the aforementioned positioning of the hydraulic adjustment unit on the camshaft turn represents a clear restriction.
With regard to the general technical background, reference is also made to German Patents DE 195 02 496 A1 and DE 196 1.5 076 C2 which have respective-corresponding U.S. applications in the form of U.S. Pat. Nos. 5,540,197 and 5,829,399 the disclosures of which are hereby incorporated herein by reference.